The Ministry for Primary Industries (MPI) is defending DairyNZ's investigation into toxic swedes which killed hundreds of cattle in Southland last spring.
DairyNZ released tests results that confirmed higher levels of glucosinilate, a compound toxic to cattle, in the stems and upper leaves of the Herbicide Tolerant (HT) swede variety.
It has warned farmers not to feed swedes to cows in late pregnancy or early lactation, but the product is still on the market.
The Green Party has criticised the government for not leading the investigation into the swedes themselves, and for not pulling the product off the shelves.
MPI spokesperson Allan Kinsella said the investigation needed to be managed day-to-day at farm level, and that made DairyNZ the right fit for the job.
"MPI has been heavily involved in the investigation and will continue to be," he said.
"MPI stepping in with direct regulatory intervention would not have been a best approach in this situation. If it was clear the deaths could be directly attributed to HT swedes as the sole cause, we would have certainly banned their use, but that wasn't the case.
"Some cows which ate the HT swedes died, and there were others which had no problems at all. Some deaths occurred in non-HT varieties as well."
Mr Kinsella said MPI was waiting on the final scientific report, expected in October, before deciding whether any regulatory controls, such as pulling the swedes off the market, were needed.